A standard lathe chuck has a spindle that is rotated at high speed and that has a head carrying a plurality of jaws that can be moved radially. The spindle is typically hollow and houses an actuating rod that is axially displaceable in the spindle and that is connected in the head to mechanism that displaces the jaws radially together when the rod is moved axially in one direction and that displaces them axially apart when moved axially oppositely. These jaws can be used to externally or internally grip a workpiece held by the chuck.
It is known to provide on the end of the spindle remote from the chuck head a transmission having a pair of coaxial input wheels rotatable about the spindle axis, an output member axially coupled to the actuating rod, and gearing interconnecting the input wheels to the output member to convert net rotation in one direction of the input wheels into axial movement in one direction of the output member, and opposite rotation into opposite axial movement. The gearing can be at least one shaft extending parallel to the spindle and having one end formed with a pinion meshing with one of the rotary input wheels and an opposite end formed with a thread engaged axially in the output member, and another gear meshing between the input wheels to make them rotate synchronously opposite each other.
In my copending patent application 473,448 filed Feb. 1, 1990 (now U.S. Pat. No. 5,005,453 I describe an adjustment apparatus used in a machine tool having a housing normally rotated about a housing axis and having a part that is axially movable relative to the housing to adjust the tool. The apparatus has a drive having a rotary drive output, a differential transmission having a rotary input connected to the drive output and a pair of transmission outputs. This transmission includes a reverser for rotation of one of the transmission outputs opposite that of the other transmission output. Respective wheels coupled to the transmission outputs are rotatable coaxially on the tool housing and respective screws are rotationally coupled to the wheels, axially fixed on the tool housing, and both threaded in the movable part of the machine tool. One of the screws is of opposite hand to the other screw.
In accordance with further features of this earlier invention the differential transmission comprises a pair of coaxial output bevel gears one of which constitutes one of the transmission outputs, a rotary input wheel between the bevel gears, an equalizing gear carried on the input wheel and meshing with the bevel gears, and a reversing gear train connected between the other bevel gear and the other transmission output. The transmission outputs are respective output transmission gears one of which is fixed directly to the one output bevel gear and the other of which is connected via the reversing gear train to the other output bevel gear. In addition the transmission has a housing and both of the transmission output gears are coaxial and carried on the same side of the housing. The transmission includes an input shaft carrying the input wheel and connected to the drive output and the one transmission output gear is coaxially carried on the input shaft and the other transmission output gear is coaxially carried on the one transmission output gear. Finally the two transmission output gears are of the same diameter as each other, the two bevel gears are of the same diameter as each other, and the wheels are of the same diameter as each other so that the transmission outputs will move identically but oppositely.
While such an arrangement is relatively effective, it has the considerable disadvantage that a multiplicity of parts are in constant relative rotation, whether they are doing any real work or not. In other words even when the chuck is set and not needing of any adjustment, the various wheels and gears are all counterrotating. Even though there is no net rotation, that is the rotation in one direction is exactly equal to that in the opposite direction, the parts are still moving and subject to considerable wear.